Splitter vane construction for turbofan engine



Nov. 8, 1966 J. A. FLIGG, JR 3,

SPLITTER VANE CONSTRUCTION FOR TURBOFAN ENGINE Filed April 28, 1965 2Sheets-Sheet 1 Nov. 8, 1966 J. A. FLIGG, JR 3,283,995

SPLITTER VANE consmucwxou FOR TURBOFAN ENGINE Filed April 28. 1965 2Sheets-Sheet z ws/v 7a,? J/QML J A F1 /66, (M

United States Patent Ofiice 3,233,995 SPLITTER VANE CONSTRUCTION FORTURBOFAN ENGINE James A. Fligg, Jr., East Hartford, Conn, assrgnor toUnited Aircraft Corporation, East Hartford, Conn, a corporation ofDelaware Filed Apr. 28, 1965, Ser. No. 451,477 3 Claims. (Cl. 230-122)This invention relates to a turbofan gas turbine engine and particularlyto the splitter that divides the air from the fan stages of thecompressor.

One feature of the present invention is the arrangement of the splitterso as to increase the stalling pressure ratio of the fan stages. Moreparticularly a feature of the invention is a splitter so positioned thata higher pressure ratio across the last fan stage will be reached beforethat stage will stall.

It has been found that the fan stage which is directly upstream of thesplitter is the limiting factor in achieving adequate fan stall. If thepressure ratio at which stalling oocurs can be raised, the fan operatingpressure ratio can be increased. Accordingly, one feature of theinvention is a splitter that will obtain a higher surge pressure ratio.

One feature of the invention is that the splitter is so located andarranged as to adjust the velocity leaving the downstream tan stage andthereby control the radial flow distribution across the last stage offan blades.

Other features and advantages will be apparent from the specificationand claims, and trom the accompanying drawings which illustrate anembodiment of the invention.

FIG. 1 is a fragmentary longitudinal sectional view through a portion ofthe compressor.

FIG. 2 is a diagram of compressor performance.

FIG. 3 is a schematic view showing the flow as affected by the splitter.

The invention as shown is applied to the compressor of a turbofan engineof the type shown by way of example in Hopper 2,979,900. In this type ofengine the first few stages of compression occur in the fan stages ofwhich the last stage represented by a row stator vanes 2 and a row ofrotor blades 4 is shown. From these fan stages the compressed air isdivided between a tan duct 6 and the remainder of the compressor stagesrepresented by spaced rows of stator vanes 8 and 10 and intervening rowsof rotor blades 12 and 14. A splitter 16 is supported from the fan ductwall 18 by straightening vanes 20 in the fan duct spaced downstream fromthe leading edge of the splitter and the compressor case 22, alsosupported by the vanes 20, supports the rows of vanes 8 and 10 in thecompressor air path, the vanes 8 also being spaced downstream from theleading edge of the splitter.

The splitter 16 thus divides the air from the fan blades into fan .air,the air from the blades between the splitter and the blade tips 24, andcompressor air which is the air from the blades between the splitter andthe roots 26 of the blades. In the arrangement shown, the compressorstages and the fan stages of blading are connected together to rotate asa unit, the disc 28 supporting the fan blades 4 and the disc 30 for thecompressor blades 12 being interconnected by a ring 32 bolted to bothdiscs. Suitable bearings position the rotor assembly within the stator,as will be apparent.

The splitter is positioned with its tip or leading edge 34 projectingforwardly beyond the vanes 8 or 20 and closely spaced from the trailingedges 36 of the row of fan blades 4. It has been found that thisspacing, to be most effective, must be a distance less than aboutonehalf the chord of the blade measured at the same radius 3,283,995Patented Nov. 8, 1966 from the compressor axis as that of the splitter.Thus, as shown in the drawing, the leading edge of the splitter isspaced close enough to give the necessary axial clearance to avoidcontact between the splitter and the blades. With the splitter closelyspaced in this manner the velocity of air entering the compressor stagesmay be determined and thus the flow of air over the fan blades 4, atleast for the portion of the blades adjacent their trailing edges, maybe controlled. By proper positioning of the splitter, for example, theve ocity of the air leaving the rotor trailing edge of the rotor blade 4may be increased. The closeness of the splitter to the blading minimizesany radial component of flow 'at the trailing edge of the fan blade 4.The result is to stabilize the flow adjacent the root end of the fanblade.

The effect of the forward extension of the splitter is shown in FIG. 2in which the solid line shows the stall line on the compressor map withthe closely spaced splitter and the dotted line shows the stall line onthe compressor map for the same compressor with a remote splitter. Inthis figure the remote splitter was 1.50 inches from the trailing endand the proximate splitter was 0.300 inch from the trailing ends of theblades. The chord of the blade at this point was 2.56 inches in theapparatus used. Since the surge pressure ratio is substantiallyincreased, it is apparent that the compressor may be operated stall thatwould occur with a remote splitter.

Tests have indicated that when the splitter has its leading edge closeto the blades, radial components of flow occur within the 'blade row,this being exemplified in FIG. 3 where the streamline shift is shown tobe radial in the trailing half of the blades thereby causing a highervelocity of air at the root of the fan rotor. This effect preventsseparation at the root and thereby delays the stall that would occurwith a remote splitter.

It is to be understood that the invention is not limited to the specificembodiment herein illustrated and described, but may be used in otherways without departure from its spirit as defined by the followingclaims.

I claim:

1. An axial flow compressor having a row of stator vanes, a row of rotorblades directly downstream of and closely adjacent to the vanes, each ofsaid blades having a root, a tip, a trailing edge, and a chord thatvaries from root to tip, and a splitter downstream of the row of bladesand located at a position radially of the rotor between the root and tipof the blade, the blades having no spanwise obstruction to the flow overthe blade adjacent to the splitter, said splitter dividing the flow fromthe blade and having its leading edge closely adjacent to the trailingedge of the blade, said leading edge being spaced firom the trailingedge of the blade a distance less than one-half the chord length of theblade at said position of said splitter whereby said splitter affectsthe radial component of flow over the surfaces of the blades.

2. An axial flow compressor having at least one stage of fan blading,including 'a row of rotor 'blades, each of said rotor blades having aroot, a tip, a trailing edge and a chord that varies from root to tip,at least one stage of compressor blading including stator vanes androtor blades downstream of the fan blading to which the fluid from aportion of the fan stage is delivered, a dividing splitter directlydownstream of the fan rotor blades concentric to the axis of the fanrotor blades and surrounding the compressor stage for directing thefluid from the inner portion of the fan blading to the compressor stage,said rotor fan blades having no spanwise obstruction to the flow overthe blade adjacent to the splitter, said splitter dividing the flow fromthe blade and having its leading edge closely adjacent to the trailingedge of the fan rotor blades, the leading edge of the splitter beingspaced from the trailing edges of the row of fan rotor blades a distance3 less than one-half the chord length of the blade at said position ofsaid splitter whereby said splitter afiects the radial component of flowover the surface of the fan rotor blades.

3. An axial flow compressor as in claim 1 in which the splitter isWedge-shape in cross section with the point of the wedge extendingupstream and forming the leading edge of the splitter, thisconfiguration of the splitter producing an increased velocity of flowinto the compressor stages and thereby an increase in the pressure ratioacross the fan blades for substantially any operating condition of thecompressor.

References Cited by the Examiner UNITED STATES PATENTS 2,046,737 7/1936Gosslau s 230-122 4 Ponomarefi 230-120 Ryan et a1. h 230-122 Rogers60-356 Fletcher 230-122 Hewson 230-116 FOREIGN PATENTS Canada.

France.

12/ 1954 Great Britain.

MARK NEWMAN, Primary Examiner.

HENRY F. RADUAZO, Examiner.

1. AN AXIAL FLOW COMPRESSOR HAVING A ROW OF STATOR VANES, A ROW OF ROTORBLADES DIRECTLY DOWNSTREAM OF AND CLOSELY ADJACNET TO THE VANES, EACH OFSAID BLADES HAVING A ROOT, A TIP, A TRAILING EDGE, AND A CHORD THATVARIES FROM ROOT TO TIP, AND A SPLITTER DOWNSTREAM OF THE ROW OF BLADESAND LOCATED AT A POSITION RADIALLY OF THE ROTOR BETWEEN THE ROOT AND TIPOF THE BLADE, THE BLADES HAVING NO SPANWISE OBSTRUCTION TO THE FLOW OVERTHE BLADE ADJACENT TO THE SPLITTER, SAID SPLITTER DIVIDING THE FLOW FROMTHE BLADE AND HAVING ITS LEADING EDGE CLOSELY ADJACENT TO THE TRAILINGEDGE OF THE BLADE, SAID LEADING EDGE BEING SPACED FROM THE TRAILING EDGEOF THE BLADE A DISTANCE LESS THAN